Four different varieties of Ashwagandha (Withania somnifera Dunal) viz.  Vallabh 01 (V01), Vallabh 02 (V02), Pratap (P), and Chetak (C) were investigated to determine the impact of elevated temperature (ET) levels on the morphology, biomass, and concentration of phytochemicals. The plants were exposed to ET (AT ± 3˚C) from November to March 2022. Results showed an increase in the shoot length (53.1% in V01 and 22.4% in V02, P, and C), and a 70% decrease in the root length of all the varieties under ET. Enhancement in the shoot biomass production (14.05, 11.3, 1.15, and 10.29% in V01, V02, P, and C) while the decline in the root biomass production (17.07, 34.6, 1.54, and 2.33% in V01, V02, P and C) were found under ET. Under ET, V01 showed a 3.6 % decrease in the phytochemical content while the other three varieties (V02, P, C) had an increase in the phytochemical content (45.2%, 10.02%, and 32.14% respectively). The ET significantly enhanced terpenoids, steroids, and alkaloids in all varieties of W. somnifera. These findings showed that V01 is most tolerant while P is sensitive to temperature stress (V01> V02> C> P). The study revealed the tolerance ability of Withania somnifera to temperature stress in the context of climate change.

Keywords: Withania somnifera, temperature stress, climate change, phytochemical profile, growth

How to cite: Singh, A. and Mina, U.: Effect of elevated temperature on the morphology and phytochemical profile of Withania somnifera’s varieties, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2213, https://doi.org/10.5194/egusphere-egu24-2213, 2024.

The olive tree is mainly cultivated in the temperate zones of the Mediterranean area. Temperature is the main factor to evaluate the climatic suitability for olive cultivation. The study of the spatial and temporal variations of temperatures in a territory is necessary to define the most appropriate areas for production, as well as to evaluate different varieties. Extremadura has more than 269,000 ha of olive trees with a production of 884,960 tonnes, the third-largest surface area, and the second-largest olive-growing production in Spain. In this study the number of olive active days (OAD), the growing degree-days (GDD), and the average temperature of the olive growing period (OGST) index are analysed. The active days for the olive tree have been defined as those in which the average daily temperatures are above 14.4 °C between April and October. The minimum and maximum daily temperatures, from the meteorological data base of the Spanish government (AEMET), located in the main olive growing areas have been used, considering a period from 1991 to 2020. Mann-Kendal test and Sen's slope have been used to determine trends and their magnitude. The results show 200 active days per year, between 185 in Ibores and 215 in Vegas del Guadiana. The mean GDD value was 1514°C, varying between 1363°C in the Ibores area and 1685°C in La Serena whith a significant increasing trend in five areas. Growing degree-days have increased by an average of 4.9°C per year. The mean OGST value was 22.0°C, varying between 21.7°C in the Logrosan-Guadalupe area and 22.4°C in La Siberia. It has also shown a significant increasing trend in the index in four areas. Temperatures in the olive tree growth period have increased by an average of 0.21°C per decade, which represents an average increase of 0.67°C between 1991 and 2020.

Keywords: olive, active days, degree-days, temperature, trends, Spain.

How to cite: Paniagua, L. L., García-Martín, A., García García, D., Aguirado, C., Rebollo, F. J., Moral, F. J., and Honorio, F.: Temperature trends  in olive growing season in producing areas of Extremadura (Spain), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3469, https://doi.org/10.5194/egusphere-egu24-3469, 2024.

The olive tree (Olea europaea L.) is one of the main woody perennial crops in Europe, especially in the Mediterranean area. The area dedicated to olive cultivation in the European Union (EU) has increased in the last decade, reaching 4.6 million hectares. Extremadura (Spain) is the region with a semi-arid Mediterranean climate located most south-west of Europe. It has a great climatological contrast in the North-South direction. Numerous studies indicate that an increase in temperatures and a reduction in precipitation is expected due to climate change in the Mediterranean region. This would cause an increase in crop Evapotranspiration and a lower contribution of rain, especially in dryland crops. Using time series of climate data (1990-2021), the differences between areas have been analyzed using an Anova and Tukey test. The trend of Evapotranspiration of the olive crop and annual effective Precipitation  in 13 olive-growing regions of Extremadura was also analyzed. To determine the monotonic trend, the Mann-Kendal test and Sen's slope estimator were used. The results showed clear differences between the olive-growing areas, for the analyzed indices. An increase in Evapotranspiration was found in important Olive-growing areas. However, the effective precipitation did not show any trend. These results contribute to the climatic characterization of the Olive-growing regions of Extremadura and could affect the yields and quality of production, requiring a varietal adaptation and cultivation techniques, as well as a change in the distribution of suitable cultivation areas.

Keywords: Olive tree, Agroclimatology, Evapotranspiration, Extremadura

How to cite: García Martín, A., Paniagua Simón, L. L., Honorio Guisado, F., Moral, F. J., Rebollo, F. J., Aguirado, C., and Rebollo, L.: Characterization of Evapotranspiration and effective precipitation in the Olive Areas of Extremadura, Spain. (1990-2021), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3949, https://doi.org/10.5194/egusphere-egu24-3949, 2024.

The increase in temperature affected the entire plant world, including the vines. These changes are reflected in the quantity and quality of the harvest, the chemical composition, and the appearance of the phenological phases of the grapevine. The shift of budding towards the beginning of the year can be particularly worrying due to the frequent occurrence of frost in the continental area of ​​Croatia. The shift of the harvest towards the warmer part of the year brings problems when storing grapes. Due to the great importance of viticulture for agriculture and tourism in Croatia, it is necessary to examine changes in the occurrence of phenological phases in current and future climatic conditions.

Due to all of the above, statistical models were developed to describe the occurrence of phenological phases. Also, the crop model STICS was parameterized for the Croatian region and four grape varieties. Bayesian statistics were also used to get an insight into the amount of earlier and later harvests. To get a clearer picture of the changes in the future climate three CORDEX Regional Climate Models (RCMs) simulations (CLMcom-CCLM4-8-17, SMHI-RCA4, CNRM-ALADIN5.3) for the Croatian domain and varieties were used in this research. All RCMs are forced by output from Global Climate Models (GCMs) with moderate (RCP4.5) and high-end (RCP8.5) greenhouse gas (GHG) scenarios. SMHI-RCA4 is driven by five different GCMs (CNRM-CERFACS-CNRM-CM5, ICHEC-EC-EARTH, IPSL-IPSL-CM5A-MR, MOHC-HadGEM2-ES and MPI-M-MPI-ESM-LR), CLM by four (CNRM-CERFACS-CNRM-CM5, ICHEC-EC-EARTH and MOHC-HadGEM2-ES, MPI-M-MPI-ESM-LR), and CNRM-ALADIN5.3 with one (CNRM-CERFACS-CNRM-CM5). All the simulations have horizontal grid spacing of 0.11◦.

The results show clear trends in the budburst and harvest shifting in Croatia, regardless of the variety. Future climate analysis indicates a further shift in the occurrence of phenological phases towards the beginning of the year (that is, an earlier occurrence). The expected shifts in budburst in the period P2 (2041-2070) compared to the period P0 (1971-2000) are more pronounced for traditional varieties ('Graševina' and 'Plavac mali'), where median differences suggest shifts of 15 days towards the beginning of the year, regardless of the RCP scenario. The results indicate a shift in budburst to early March, which is a particular threat for white varieties that are mostly grown in continental parts of Croatia where low temperatures and frost in March can reduce most of the harvest. In addition, the results indicate a further shift in harvesting in the future climate, and an increase in the number of early harvests, and a decrease in the number of later harvests, regardless of location and variety. The reduction in later harvests is the most significant and can be expected in the range of approximately 30-75%. So, according to the results, in the 30-year period (2041-2070) 30-75% of the years will no longer have the later harvest that took place in the period 1971-2000.

How to cite: Omazić, B., Telišman Prtenjak, M., Kvakić, M., Meštrić, J., Bubola, M., Prša, I., and Karoglan, M.: Changes in grapevine budburst and harvest dates in Croatia under current and future climate conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4051, https://doi.org/10.5194/egusphere-egu24-4051, 2024.

Vegetation phenology is a critical indicator of terrestrial carbon and water dynamics; therefore, it is essential to understand its sensitivity to the changing climates, especially to rising temperatures. A wide range of phenological responses can be explored in urban areas where anthropogenic activities elevated temperatures as well as artificial lights. In this study, we analyzed one decade (2012 - 2021) of data on surface temperature, phenology, and land cover from the Moderate Resolution Imaging Spectroradiometer (MODIS) and artificial lights at night (ALAN) data from the Visible Infrared Imaging Radiometer Suite (VIIRS) over the capital of South Korea and its surroundings. We calculated urban cover fractions (UCF) and estimated the long-term trends of the start of the season and the end of the season (ΔSOS and ΔEOS) and the temperature during the SOS and EOS (ΔT_SOS and ΔT_EOS) and in the ALAN (ΔALAN). We then investigated how much of those factors (i.e., ΔT, ΔALAN, and UCF) contributed to the ΔSOS and ΔEOS and explored temperature sensitivities of the ΔSOS and ΔEOS under different conditions. We found that the SOS appeared to advance by three days per decade (p = 0.068), while the EOS was delayed significantly (p < 0.001) by four days per decade over most of the study region. We also noticed that 70% of ΔSOS was primarily attributed to UCF, while ΔT_SOS drove the rest. For the ΔEOS, the influence of ΔALAN appeared to be substantial (26%), with ΔT_EOS having a similar contribution level (31%). We show that the temperature sensitivity of ΔSOS is higher by 4.5% in the highly urbanized areas, and the temperature sensitivity of ΔEOS is 4.3% higher in the regions with increasing lights. Our results suggest that vegetation phenological response to the increasing temperature would become complicated with the increases of urban-like conditions (i.e., higher levels of CO₂ concentration), therefore highlighting the importance of further studies for a better understanding of terrestrial vegetation responding to the changing climates.

This study is supported by the National Research Foundation of Korea (NRF) grants funded by the Korean government (MSIT) (2020R1C1C1014886 and 2022R1C1C2009543), the Korea Agency for Infrastructure Technology Advancement (KAIA) grant funded by the Ministry of Land, Infrastructure, and Transport (22CTAP-C163540-02), and the Korea Environment Industry & Technology Institute (KEITI) funded by Korea Ministry of Environment (2022003640002).

How to cite: Kim, J., Sohn, S., and Kim, Y.: Phenological responses to urban heat and light in the Greater Seoul area , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4891, https://doi.org/10.5194/egusphere-egu24-4891, 2024.

Understanding drought, or wetness, conditions is essential not only for the rational use of water resources but also for explaining landscape and ecological characteristics. Climate change is expected to lead to an increase in aridity in many parts of the world. In semi-arid regions with warm climates, aridity poses a significant hazard, leading to the potential for desertification due to increased precipitation variability and prolonged droughts. Aridity indices can be employed to identify areas susceptible to desertification. In order to analyse the distribution of aridity in Extremadura, particularly in the areas covered by the olive oil denominations of origin in this region (the cultivation of olive trees is of great economic and social importance in Extremadura), the De Martonne aridity index (I_DM) has been used. Temperatura and precipitation data from 81 weather stations located throughout Extremadura, within the 1951–2010 period, were utilised to calculate I_DM at every station. Later, the I_DM was mapped using an integrated Geographic Information System (GIS) and a multivariate geostatistical approach (regression-kriging) that incorporated comprehensive secondary information on elevation. Annual an seasonal I_DM-kriged maps were generated. Finally, temporal trends were analysed using the Mann-Kendall test, and the Sen’s estimator was utilised to estimate the magnitude of trends. An increase in aridity, as the I_DM decreased, was apparent during the study period, mainly in the more humid locations of the north. An increase of the seasonal I_DM was also found, but it was only statistically significant in some locations in spring and summer, with the highest decreasing rate in the north of Extremadura. Although the denominations of origin in the north of the region have higher decreasing rates, leading to a drier climate, the areas in the centre and south of the region and, in consequence, the denominations of origins within these areas, with more arid climates, can be more seriously affected by the increasing aridity.

Keywords: Aridity; Climate Change; De Martonne aridity index; Extremadura; Olive tree.

How to cite: Moral García, F. J., Rebollo Castillo, F. J., Aguirado Montero, C., Rebollo Moyano, L., García Martín, A., Paniagua Simón, L. L., and Honorio Guisado, F.: Spatial analysis of the annual and seasonal aridity trends in the Main Olive-Growing Areas of Extremadura (southwestern Spain), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5594, https://doi.org/10.5194/egusphere-egu24-5594, 2024.

Climate is considered one of the most influential factors in vegetative development, formation and quality of fruits. The study based on bioclimatic indices and the orography of a territory makes it possible to evaluate its suitability for a specific crop and find areas with particularities. This study shows the analysis and trend of the Number of Days with Optimal Temperatures for Carbohydrate Synthesis (NDCHS), in the 12 olive-growing areas (270,000 ha) of Extremadura (Southwest of Spain). Based on the average daily temperature of the 75 climatic stations located in the olive-growing areas, the NDCHS was calculated for the period 1990-2021. To determine the trend, the Mann-Kendal test and Sen's slope estimator were used, and the Pearson test was used to obtain the correlation between the climatic variables. The results show an annual average of 111 days for the NDCHS. The minimum value was found in Ibores with 100 days and the maximum in Vegas del Guadiana with 120 days. The Pearson correlation obtained a maximum value of 0.848 with the average temperature. The Mann-Kendall test showed significant increasing trends in 8 of the 12 olive-growing areas with a minimum of 0.34 (Sen's slope) in Logrosán-Guadalupe and a maximum of 0.76 for the regions of Alburquerque and Vegas del Guadiana. A general average increase of 0.54 NDCHS per year was found for the olive-growing regions in the period studied.

Keywords: Olive tree, Extremadura, olive-growing areas, carbohydrates

How to cite: Honorio Guisado, F., Aguirado Montero, C., Paniagüa Simón, L. L., García Martín, A., Rebollo Moyano, L., Rebollo Castillo, F. J., and Moral García, F. J.: Analysis of the optimal temperatures for the synthesis of carbohydrates during the productive period of the olive tree in the olive-growing areas of Extremadura, Spain., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6105, https://doi.org/10.5194/egusphere-egu24-6105, 2024.

The phenology of wine grapes has emerged as a crucial aspect for comprehending and forecasting the impacts of climate change on viticulture. This is due to phenology being essential in evaluating the suitability of grape varieties to future conditions. However, there is still a lack of quantitative characterization for key phenological stages in a majority of indigenous wine grape varieties from Spain and Portugal. Here we analyze the phenological responses to climate of predominant grape varieties in the Iberian Peninsula, including Tempranillo, Airen, Garnacha, Macabeo, and other varieties like Albariño, Godello, Pedro Ximenez, Fernão Pires (Portugal), which are extensively cultivated in specific regions. We compiled a comprehensive dataset from research centers and specialized organizations such as Origin Denominations across the Iberian Peninsula. The recorded field observations were then compared against well-established agroclimatic indices, such as Growing Degree Days (GDD), days with maximum temperature above 35°C, or days below 10ºC, amongst others. Even within our limited set of varieties, we observed surprising diversity in responses, supporting phenology-based varietal selection as an adaptive solution. This underscores the necessity to continue documenting phenology for many other locally understudied varieties. Our findings fill a knowledge gap, contributing to ongoing efforts in refining varietal selection strategies for adapting viticulture to climate change.

How to cite: Fernandez Pastor, M. and the Iberian Future Wines Research Team: Phenological characterization of major winegrape varieties in the Iberian Peninsula, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6333, https://doi.org/10.5194/egusphere-egu24-6333, 2024.

Phenological events in temperate plants are highly dependent on external factors such as temperature and photoperiod, but also on internal factors linked to the plant's development. Recent studies have demonstrated a strong correlation between the timing of autumn leaf senescence in temperate trees and temperature conditions before the summer solstice that alter the rate of plant development. However, experimental evidence to specifically test this hypothesis is lacking. Here, we examined how accelerated growth in early summer induced by warmer temperatures affects the timing of senescence in three common European trees: Carpinus betulus, Tilia cordata and Acer platanoides. Potted saplings were grown under "ambient" open top chambers (OTCs), i.e. with similar temperature as outside the OTC, and under actively warmed OTCs, i.e. +5°C above the ambient, from January until the summer solstice. At the summer solstice, all the potted trees were transferred to an unheated greenhouse, sharing the same climatic conditions until leaf fall in autumn. Plant diameter and height were measured before bud burst, at the summer solstice and after leaf senescence. In addition, gas exchange measurements were conducted before and after the summer solstice to assess leaf performance. Finally, leaf senescence was measured weekly, visually and using a chlorophyll meter, from August until leaf fall.

Leaf-out dates were strongly advanced in the warming treatment for all species (14–28 days). Primary growth was not affected by warming for any species whereas secondary growth was significantly enhanced in the warming treatments for C. betulus and T. cordata. Interestingly, the initiation of leaf senescence occured significantly earlier for the saplings that were subjected to warmer temperature in early summer for C. betulus and T. cordata but not for A. platanoides, suggesting an effect of secondary growth rate during early summer in regulating the start of leaf senescence. Chlorophyll content, photosynthesis and SLA also showed significant differences between the two temperature conditions applied in early summer for C. betulus and T. cordata, even when measured several months after their transfer to the same conditions. Specifically, at the end of summer, leaves that were exposed to the warming treatment in early summer were less efficient for carbon assimilation, had lower chlorophyll content, showed higher SLA (T. cordata only) and started coloration earlier than the ones kept under ambient conditions during early summer.

Our results suggest that there is a strong link between growth development in spring and the timing of leaf senescence onset in autumn as recently shown at large scale in the northern hemisphere. More studies focusing on molecular and/or on tree physiological mechanisms should be conducted to identify the underlying mechanisms responsible for the link between secondary growth rate in early summer and the onset of leaf senescence. 

How to cite: Vitasse, Y., Ren, S., Grossiord, C., Walde, M., and Zohner, C.: Enhanced secondary growth induced by warmer temperatures in early summer advances autumn leaf senescence in temperate saplings, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7233, https://doi.org/10.5194/egusphere-egu24-7233, 2024.

How to cite: Meštrić, J., Telišman Prtenjak, M., Omazić, B., and Kvakić, M.: Parameterization and verification of the STICS model for grapevines in the region of Croatia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8438, https://doi.org/10.5194/egusphere-egu24-8438, 2024.

Using remote sensing data to assess plant phenology is a useful method for monitoring areas at larger spatial scales. One of the most widely used methods for analyzing changes in the timing of the growing season is the employment of vegetation indices and phenological metrics (phenometrics) derived from them. Using phenometrics, it is possible to evaluate changes in the growing season for different land covers and different environmental conditions not only at the local level but also in larger areas. At the larger scales, the meteorological conditions and especially their influence on plant phenology can be more diverse. For the determination of basic phenometrics (the start of the growing season (SOS), the end of the growing season (EOS), and the length of the growing season (LGS)), we used Enhanced Vegetation Index2 (EVI2) derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) imagery. Phenometrics and their trends were calculated for four different land covers (arable land, broad-leaved forest, coniferous forest, and grassland) in the time period from 2000 to 2022 in the central European region. Furthermore, the changes in the timing of the growing season were calculated in different altitude and environmental zones and their trends were compared with meteorological variables (e.g., minimum and maximum air temperature, length of day, global radiation, precipitation, soil moisture, etc.). Based on this analysis, the main factors influencing phenological changes for different land covers were evaluated in different environmental conditions.

Acknowledgment: This work was supported by the Ministry of Education, Youth and Sports of the Czech Republic (grant AdAgriF - Advanced methods of greenhouse gases emission reduction and sequestration in agriculture and forest landscape for climate change mitigation (CZ.02.01.01/00/22_008/0004635).

How to cite: Dížková, P., Bartošová, L., Poděbradská, M., Bláhová, M., Fischer, M., Semerádová, D., Balek, J., Hájková, L., Žalud, Z., and Trnka, M.: Analysis of meteorological variables influence on the growing season in Europe, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10021, https://doi.org/10.5194/egusphere-egu24-10021, 2024.

The impact of climate change on phenological timing is well-known and described in the scientific literature. Most papers agree that rising temperature accelerates the onset of spring phenological phases. Nevertheless, there is more significant disagreement in the synchronicity or asynchronicity of phenological trends of individual species. In this study, therefore, we will work with long-term phenological data that have been observed continuously in floodplain forests (and relate to herbs, shrubs, trees, and bird populations) from 1961 to the present. The observed plants and bird species showed statistically significant (p < 0.05) shifts in phenological terms to an earlier year. Still, the rate of the shift among the observed species differed. The most progressive shifts were detected for the herbs (2.3 days per decade), followed by the shrubs (2.2 days per decade), trees (1.4 days per decade), and finally, the bird species (also 1.4 days per decade). There are many changes in trends within the specific species group – e.g., quite a considerable variability was detected for herbs – the phenophase ´full flowering´ trend is moving between 1.3 and 3.3 days per decade. For this reason, we also include the role of pollinators within this study - bumblebees (Bombus) as a new input to the phenological observations to see if there is any asynchrony between these early spring species.

Acknowledgment: This work was supported by the Ministry of Education, Youth and Sports of the Czech Republic (grant AdAgriF - Advanced methods of greenhouse gases emission reduction and sequestration in agriculture and forest landscape for climate change mitigation (CZ.02.01.01/00/22_008/0004635).

How to cite: Bartošová, L., Dížková, P., Bauerová, J., Balek, J., Křenová, Z., Svobodová, E., Bláhová, M., Hájková, L., Možný, M., Žalud, Z., and Trnka, M.: Phenological variability between species of floodplain forests and the role of the pollinators, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16853, https://doi.org/10.5194/egusphere-egu24-16853, 2024.

Estimating climate-change-induced changes in biological systems, e.g., tree phenology, requires long, consistent and reliable datasets. Phenology observations within meteorological and other ground observation networks provide invaluable data but are of limited geographical distribution and observational range. Remote sensing observations surpass such problems and have been extensively used in phenology research, but suffer from other issues such as coarse spatial resolution, relatively long observation repeat cycles, issues due to clouds, short observational time series, etc. Those issues limit the number of remote sensing platforms which are suitable for the analysis of possible changes in the phenology of forest tree species at a local or regional level. NDVI derived from the MODIS daily measurements of reflectances at 250 m resolution spanning from 2000, in combination with tree species distribution maps from forest management plans, might be an optimal tool for investigating recent shifts in species-specific tree phenology at a local or regional level. Increased frequency of climate extremes, such as late spring cold spells, combined with the sensitivity of deciduous trees to frost damage during leaf unfolding and flowering, threatens the health and regeneration capacity of forests. The possible decoupling of tree and animal phenology additionally strains the entire forest ecosystem. These problems are exacerbated in urban and peri-urban forests, such as forests in Mount Medvednica Nature Park, Croatia, which are of major importance to the well-being of the people living in the Zagreb metropolitan area. Urban and peri-urban forests are exposed not only to the effects of climate change but also to the negative effects of pollution and the ‘urban heat island’ which all affect the timing and duration of leaf unfolding. 
Our research aims to quantify the changes in the spring phenology of Mt Medvednica’s forests during the period 2000–2020 using MODIS NDVI at 250 m, local forest management maps with tree species distribution information, and a digital elevation model. Our results show a delay in the Start of Season (SOS) with the overall trend of 0.12 days·yr^-1, but only due to SOS delay in common beech (F. sylvatica, 0.13 day·yr^-1), which might be a consequence of delay in meeting the chilling requirement needed to end the dormancy. Other deciduous tree species showed no significant trend in SOS. On the other hand, the End of Green-up (EOG) occurred sooner for all investigated tree species, with an average trend in EOG of –0.18 days·yr^-1 (F. sylvatica and Q. pubescens, –0.17; Q. cerris,  0.21; Q. petrea and Castanea sativa, –0.23 day·yr^-1). Consequently, during the 21 years of observation, the duration of leaf development of Mt Medvednica’s forests was on average shortened by 6.5 days.

Keywords: phenology, leaf unfolding, MODIS, NDVI, peri-urban forests, Mount Medvednica.

Acknowledgements:
The research has been supported by the Croatian Science Foundation project MODFLUX (HRZZ IP-2019-04-6325), by the Hungarian Scientific Research Fund (OTKA FK-146600) and by the TKP2021-NVA-29 project of the Hungarian National Research, Development and Innovation Fund. We thank to Croatian Forests Ltd. for granting access to their forest database and Croatian Meteorological and Hydrological Service for providing meteorological data.

How to cite: Marjanović, H., Kern, A., Anić, M., Bitunjac, D., and Ostrogović Sever, M. Z.: Detecting species-specific changes in spring phenology of Mt Medvednica forests using NDVI obtained from remote sensing with MODIS , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13418, https://doi.org/10.5194/egusphere-egu24-13418, 2024.

Knowing and understanding variation in plant phenology is important for three main reasons. 1. Plant phenology is sensitive to climate change, 2. Plant phenology influences the dynamics and interactions between species, and 3. It drives important ecosystem functions. Still, large-scale, macroecological analyses spanning several phenological databases from various continents and environmental conditions are scarce.

Here we present the first results of a global analysis of the relationship between phenological events and functional traits in herbaceous plant species as a basis for predicting variations in ecosystem functions. More specifically, we analyzed phenological data from three different data sources: the PEP725 database from Europe, the NPN database from the US, and the PhenObs database from a global network of botanical gardens (www.idiv.de/en/phenobs). We evaluate spatio-temporal variations of three phenological stages: leaf emergence, open flowers, and onset of senescence. We linked phenological variations in space as well as phenological variations in time with variations in temperature (extracted from CRU TS database v4.07) of the observation periods and observation sites, respectively. Deduced associations between phenology and temperature across time and space were compared between Europe and North America, and between controlled environments in botanical gardens and natural environments.

First results indicate that the direction of phenological responses to changes in temperature is consistent across time and space. However, the variability of this response is higher across time compared to space. This higher variation phenology is not explained by differences in variations of temperature, but we assume that other environmental and climatic factors could vary more strongly across the spatial compared to the temporal gradient. The phenological responses of plants growing in botanical gardens to increasing temperature, were less variable compared to plants growing in uncontrolled environments. We attribute these differences to botanic garden management, such as irrigation, which mitigates the effects of increased temperature and drought on herbaceous species phenology. On our poster, we will further determine the climatic factors and functional traits that explain inter- and intraspecific phenological variability.

How to cite: Silva-Cala, A. L., Rauschkolb, R., Bucher, S. F., Kattge, J., Zaehle, S., and Römermann, C.: Are space-for-time substitution approaches appropriate in phenology research? Results from a macroecological approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17609, https://doi.org/10.5194/egusphere-egu24-17609, 2024.

Catalonia has been experiencing the most important drought since, at least, 1970. This three-year drought has not experienced any significant precipitation episodes and has particularly affected terrestrial ecosystems.

The Mediterranean vegetation, adapted to periods without rain, overcame the first year of drought (2021) without great phenological impact beyond specific places and individuals.

In the second year of drought (2022), the lack of water affected sprouting, fruiting, and leaf senescence, such as lower fruit productivity and smaller-than-normal fruit size.

During the third year of drought (2023), the strong water stress has directly threatened the survival of some monitored species. The ones that have not died present several phenological anomalies such as lack of flowering (with the consequent absence of fruit), minimal foliation, and drying of branches of the entire individual.

Such resilient species as holm oak, almond tree, grey-leaved cistus, olive tree, strawberry tree and grape have been affected. In the inland agricultural area of Catalonia irrigated by the Canal d'Urgell, there has been an obligation to limit support irrigation to a minimum to keep trees alive, which has caused the loss of the harvest in many places.

These three years without rain have been accompanied by an increase in the average temperature which has advanced ripening. Abnormally warm autumns have led to second blooms or re-sprouting of leaves (grape and shadow plane tree, for example). The mild temperature of the 2023 winter has complicated the structural pruning of the vine and other fruit trees due to the absence of the physiological winter stop.

How to cite: Busto, M. and de Yzaguirre, X.: Consequences of three years of drought in Catalonia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18358, https://doi.org/10.5194/egusphere-egu24-18358, 2024.

Forests and atmosphere interact, for example when trees assimilate and respire CO₂ during photosynthesis. Depending on their productivity and net assimilation, forests may function as a carbon sink or source. Further, the amounts of synthesized sugars assigned to growth, reproduction, and defense affect the fitness of the trees and eventually the distribution of species. Climate strongly impacts such forest-atmosphere interactions, which affect forests and in turn feed back to the climate.

For deciduous trees, the beginning and end of the photosynthetically active pe­riod (i.e., the ‘growing season’) relate to spring and autumn leaf phe­nology (i.e., leaf unfolding and leaf senescence), respectively. The climatic conditions during the growing season (i.e., the ‘bioclimate’) are directly and indirectly influenced by climate change, as climate change alters the timing and length of the growing season through shifts in leaf unfolding and leaf senescence. While past changes in leaf unfolding and leaf senescence can be analyzed by in-situ observations, the underlying drivers and particularly possible future changes are often studied with pro­cess-oriented models. However, these models may suffer from a bias to­wards the mean (BTM), which causes the simulated values to be closer to the average than the observations and could result in overly flat simulated trends.

Here I discuss (1) changes in the growing season and bioclimate in Switzerland during recent decades, (2) impacts of the calibration approach on the performance of 21 leaf se­nescence models tested with observations from Central Europe, and (3) effects of the BTM in these models on their performance and projections. Growing seasons have predominately lengthened at elevation-specific rates, which was primarily caused by changes in leaf senescence and increased the number of days with a negative atmospheric water balance at low elevations. Calibrations with the Gen­eralized Simulated Annealing algorithm and with systematically balanced or stratified samples yielded the best performing leaf senescence models, while their performance was most influenced by their structure. The BTM caused the performance of current leaf senescence models to be only slightly better than the performance of a null model that constantly simulates the average of the calibration sample. Standard model comparisons favored models with stronger BTM, while models with weaker BTM projected smaller backward shifts in future leaf senescence. The latter is counter-intuitive, since smaller shifts result from flatter trends and are therefore associated with stronger rather than weaker BTM.

I conclude that (1) the effects of phenological changes on the bioclimate should be considered when studying past and future forest productivity and species composition, (2) inference from process-oriented models to the underlying processes and drivers of leaf senescence is valid, and (3) current leaf senescence projections are highly uncertain and thus unreliable. While it is likely that current projections of future biosphere behavior under global change are distorted by erroneous state-of-the-art leaf senescence models, there is ample need and potential for the development of more accurate process-oriented models.

How to cite: Meier, M.: Climate change-induced shifts in leaf phenology of trees: past and future trends, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18968, https://doi.org/10.5194/egusphere-egu24-18968, 2024.

Land surface phenology (LSP), the study of seasonal dynamics on the vegetated land surface from satellite data, has contributed to improve the understanding of the phenological dynamics of vegetation in boreal and temperate ecosystems located in the high and mid-latitude regions of the Northern Hemisphere. Iberian Peninsula is one of the most biologically rich regions of the European continent, where endemic plant species are very common. Hence, the ecosystems of the Iberian Peninsula provide a wide variety of ecosystem services, which may be altered by changes in climatic conditions. LSP has not been studied in detail in the Iberian ecosystems. Despite their ecological importance and vulnerability to climate change, there is a lack of an exhaustive and long-term characterisation of the phenological patterns of the main natural vegetation land cover types of the whole Iberian Peninsula. Therefore, the goal of this study was to monitor the LSP dynamics across major natural vegetation land cover types in the Alpine, Atlantic, and Mediterranean biogeographical regions of the Iberian Peninsula. Two-band Enhanced Vegetation Index (EVI2) time-series were generated from the MOD09Q1 surface reflectance product from January 2001 to December 2021. This MODIS product is based on 8-day image composites at a spatial resolution of 250 meters. The methodology to estimate LSP from raw EVI2 time-series followed two steps, including a) data denoising and b) the extraction of spring and autumn phenometrics. A double logistic function was used to smooth the EVI2 time-series from TIMESAT software. Start of the growing season (SOS) (i.e., proxy of the spring phenology) and the end of the growing season (EOS) (i.e., proxy of the autumn phenology) were extracted using a 10% threshold-based technique.

Results of this research showed spring and autumn phenometrics had a similar spatial pattern across major natural vegetation land cover types of the three biogeographic regions of the Iberian Peninsula. Generally, SOS dates were in March-April, while EOS dates were in November-December. Despite this, the spatial patterns of LSP were very different in Mediterranean shrublands, savannahs and grasslands. SOS and EOS dates showed the highest variability in these natural vegetation land cover types. The growing season generally started between October and February (SOS) and ended between June and November (EOS). The spatial variability of spring and autumn phenometrics in these three natural vegetation cover types may be related to several factors: i) the mixture of the phenological cycles of different functional vegetation types (e.g., herbaceous, shrub or tree vegetation); ii) the mixture of phenological trajectories of multiple plant species; iii) the influence of non-vegetation cover, such as bare soil, affecting spectral information. These LSP patterns of natural vegetation cover types in the Iberian Peninsula could contribute to improve the understanding of the response of Iberian ecosystems to climate change.

How to cite: Caparros-Santiago, J. A., Garcia-Perez, M. A., and Rodriguez-Galiano, V.: Land surface phenology across major natural vegetation land cover types and biogeographical regions in the Iberian Peninsula, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19657, https://doi.org/10.5194/egusphere-egu24-19657, 2024.

Changing environmental conditions caused by climate change, eutrophication, and other anthropogenic factors affect the timing, duration, and surface extent of lake algae blooms across the globe. It remains, however, challenging to quantify the relative impacts of different environmental changes on the timing and characteristics of lake algae blooms, and to detect phenological trends over time, as these blooms vary considerably from year to year. Global data sets that may allow us to study algae-bloom properties along a wide range of environmental conditions and years are needed to address these challenges.

For this study, we developed such a data set using satellite remote sensing. We analyze the phytoplankton phenology of 2025 lakes across a wide range of climate zones over a period of approximately 20 years. More specifically, we used daily lake chlorophyll estimates derived from MERIS and OLCI data to extract phenology metrics (e.g. the onset and decline of peaks in chlorophyll concentration) for individual pixels within each of the 2025 lakes. Through a newly developed method, we determined the timing of blooms, i.e. clusters of peaks in different pixels occurring within the same lake during the same period of the year, and, subsequently, studied the change in the timing, duration, and size of those blooms across years.

This will, ultimately, help us to get a better overview of the extent to which lake algae blooms have changed across the globe, to attribute those changes to anthropogenic drivers, and to develop effective environmental policies to combat those changes where needed.

How to cite: Lever, J., Simis, S., Liu, X., Gilarranz, L. J., D’Odorico, P., Ginzler, C., Psomas, A., Damm, A., Gessler, A., Vitasse, Y., and Odermatt, D.: Towards a global, remotely sensed monitoring of lake phytoplankton phenology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22513, https://doi.org/10.5194/egusphere-egu24-22513, 2024.

Trees inhabiting seasonal climates organize their life cycle activities following an internal program termed phenology. The rising temperature through global warming has substantially influenced the timing of these phenological events, most prominently studied through the advancement of leaf emergence. Moreover, changes in precipitation patterns have led to severe drought events that have increased in both intensity and frequency worldwide. Both trends necessitate trees to adjust and synchronize their annual cycle within the ‘window of opportunity’ presenting itself based on favourable temperature and available soil moisture. Depending on when critical water limitations occur, tree species are affected at different developmental stages throughout their seasonal cycle. Thus, the severity of impact at a given stage and/or the flexibility to shift developmental and growth activities determine whether the same stressor results in mortality or minor growth reductions.

We used over 1000 saplings of six North American tree species (Sequoia sempervirens, Pinus contorta, Quercus garryana, Betula papyrifera, Prunus virginiata, and Acer macrophyllum) to investigate how flexibly (or conservatively) trees re-arrange (or stick to) their phenological sequence and growth activities when impacted by a) drought or b) defoliation events. Both treatments were applied separately at three different times (after leaf emergence, at the summer solstice, and in August) on different batches of saplings. The saplings were grown in a Polytunnel in Vancouver, BC, Canada without water limitations (except for the periodic drought treatments) and were equipped with magnetic dendrometers to monitor radial growth along with observations of bud development and shoot elongation. After harvest, we assessed total root and shoot biomass. In addition, through an image analysis of micro stem slices (utilizing a microtome), we were able to review the xylem properties (e.g., the number of cells produced, vessel size) of treated and control saplings.

Our findings reveal how artificial downregulation of source and sink activities at different points in the growing season impacts the performance of radial and apical meristems. Furthermore, we identify the potential of temperate tree species to cope with environmental stressors by optimally utilizing the available ‘time window of opportunity’—for instance, by shifting or splitting their phenological development and growth activity around a drought period. Finally, we discuss how these characteristics correlate with a species’ strategy and the level of bud determinism, i.e., whether shoots continue to grow later in the season (neo-growth atop pre-formed tissue).

How to cite: Baumgarten, F. and Wolkovich, E.: Phenological plasticity: shifting growth and developmental phases of North American tree species in response to environmental stressors, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22525, https://doi.org/10.5194/egusphere-egu24-22525, 2024.

Plant phenology, the study of recurring plant life history events’ timing, is a key indicator of global environmental change and significantly impacts ecosystem functions and services. Land surface phenology (LSP) characterizes plant phenology by monitoring seasonal plant canopy structure dynamics via satellites. Numerous studies have demonstrated that ecosystem-scale LSP variability is mainly driven by climate and environmental conditions across different ecosystems. However, significant spatial and temporal phenological variations are still observed within local landscapes where environmental conditions are relatively similar. This suggests that biotic factors may be important to regulating LSP variability, but their role in determining phenological variability has been underexplored. To address this knowledge gap, we selected four temperate forest sites with minor topographic relief to ensure the homogeneity of environmental conditions and examined how functional traits regulate intra-site spatial and temporal LSP variability. We combined plant functional traits derived from remote sensing data with multi-year Harmonized LandSat-Sentinel-2 (HLS) data to investigate the effects of functional traits on phenological variability. For spatial LSP variability, we assessed the extent to which functional traits could explain the variation in the start of season (SOS) and end of season (EOS). We found that functional traits showed a substantial explanatory power for spatial phenological variability across all the study sites, with cross-validation correlations (cv) ranging from 0.50 to 0.85. For temporal LSP variability, we used multi-year series of the two band Enhanced Vegetation Index (EVI2) to calculate the cumulative deviation of EVI2 values from their long-term means, which served as an indicator of temporal phenological variability. Functional traits also significantly contributed to the temporal variability across all sites, with cv ranging from 0.46 to 0.71. Furthermore, our results show that plant traits related to vegetation competitive ability and productivity (e.g., canopy height, plant area index, and leaf mass per area), are crucial to explaining intra-site phenological variability, but their relative contributions vary among different sites. Collectively, these results demonstrate that functional traits play a critical role in regulating intra-site spatial and temporal LSP variability, and plants employ diverse strategies to cope with the environment, which ultimately impacts various ecological processes.

How to cite: Zhao, Y., Wang, Z., Yan, Z., Moon, M., Yang, D., Meng, L., Bucher, S. F., Wang, J., Song, G., Guo, Z., Su, Y., and Wu, J.: Exploring the role of functional traits in regulating the spatial and temporal variability in land surface phenology across temperate forests, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15091, https://doi.org/10.5194/egusphere-egu24-15091, 2024.

A phenology project was launched in 2020 in the Eastern Townships region of southern Quebec, Canada, with the help from students from Bishop’s University. Initially, one of the main goals was to boost local phenology observations and gather data that will become useful in the future to document the impacts of climate change. We also wanted to pair the pollen monitoring programme that exists in Sherbrooke since 2006 with directs phenological observations of the local vegetation. The other goal of TreeTraque is to increase people's awareness of the impacts of climate change on vegetation.

Riding on the momentum generated by the recent adoption of the politique de l’arbre (tree- or greening policy) by the city of Sherbrooke and by the push from numerous conservation organizations within the region, we are now adding a knowledge mobilization component to the project. We wish to reach the genera public more broadly to educate them about the importance of trees in the urban environment: they combat the urban heat island effect, capture atmospheric pollution, and enhance the esthetics of a neighbourhood. A few greening programs are already in place in Sherbrooke, however, they only aim at planting trees on institutional, industrial and commercial lots. It appears important to raise awareness among the general population, especially homeowners. Indeed, in some neighbourhoods, we see that numerous owners choose not to have trees on their property or prefer shrubs or plants that do not provide any shade on buildings, streets or driveways. Our long-term objective is to create more shade to help combat the urban heat island effects and reduce the impacts of future heat waves.  

How to cite: Levac, E. and Courtemanche, B.: Phenology and knowledge mobilization about the importance of trees in urban environments in southern Quebec, Canada, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14009, https://doi.org/10.5194/egusphere-egu24-14009, 2024.